Fluid shock front sheet material engaging means



1966 R. T. SWTH, JR 3,263,886

FLUID SHOCK FRONT SHEET MATERIAL ENGAGING MEANS Filed Nov. 20, 1963 5 Sheets-Sheet .1

52 3Q 36 I 42 f 34 as 0 f 1 46 9A SOURCE INVENTOR ATTORNEYS Aug. 2, 1966 R. T. SMITH, JR 3,263,836

FLUID SHOCK FRONT SHEET MATERIAL ENGAGING MEANS 3 Sheets-Sheet 2 Filed Nov. 20, 1963 H ATMOSPHERE ATMOSPHERE F igo 4A Fig. 4

Aug. 2, 1966 R. T. SMITH, JR 3,263,886

FLUID SHOCK FRONT SHEET MATERIAL ENGAGING MEANS Filed Nov. 20, 1963 5 Sheets-Sheet 5 Delaware Filed Nov. 20, 1963, Ser. No. 325,035 15 Claims. (Cl. 226-95) The present invention relates to a means for causing magnetic tape or similar web material to be either engaged by or disengaged from a surface such as that found on a tape capstan driving system. More particularly, the invention comprises the cooperative combination within a capstan or the like of a converging-diverging nozzle with a nozzle exit pressure controlling means to produce and move a shock front which effects an appropriate pressure differential across the magnetic tape.

Pneumatic or other fluid tape capstans or the like in the prior art generally require mechanical valve mechanisms, such as a spool valve, for selectively interconnecting any one of several different pressure sources to one side of a tape in order to either force it into contact with a surface or move it away therefrom. These different pressure sources usually comprise positive pump means for providing pressure greater than the tape environmental pressure, and vacuum pump means for providing a pressure lower than the tape environmental pressure. The speed of response of such a conventional valve mechanism is limited by the relatively large inertia of the valve as well as the distance it must travel to effect the different pipe interconnections. The present invention, however, concerns means using only one air source whereas a shock wave front is selectively moved to one of several positions in a converging-diverging nozzle so as to apply pressure greater than or less than atmosphericpressure to the tape. This requires only a very small rapid movement of a mechanical valve element. Furthermore, besides the faster mechanical switching there is also faster fluid switching since there is less volume of fluid change required when utilizing the movable shock wave principle. The present invention is further advantageous since, by having fewer parts with lower tolerances, it is cheaper than the conventional prior art valve mechanism. Another advantage is that the present invention lends itself to a sufficient degree of miniaturization so that it becomes quite compatible with data processing systems utilizing pure fluid amplifier components.

It is therefore one object of the present invention to provide a web gripping device in which a shock wave front within a converging-diverging nozzle is longitudinally moved so as to change the pressure differential across the web from one polarity to the opposite polarity.

Another object of the present invention is to provide a movable shock Wave front web driving capstan or the like wherein a novel mechanical valve means is employed which is stable in any one of several positions to which it is moved by an actuating signal.

A further object of the present invention is to provide a multistable novel valve subcombination per se for controlling the exit back pressure of an orifice or the like 'by means of pulsed, rather than continuously applied, actuating signals.

These and other objects of the present invention will become apparent during the course of the following description to be read in view of the drawings, in which:

FIGURES 1 and 2 are respectively side and end elevation views of the novel movable shock wave front web engaging means;

FIGURES 3A, 3B, and 3C illustrate the principle of States Patent wave capstan members or the like.

In FIGURES 1 and 2, a stationary support body 10 is shown in which is formed a fluid conduit 12 having a converging entrance section 14 smoothly fairing into a diverging exit section 16 so as to form a restricted throat 18 therebetween. Sections 14 and 16 together comprise a converging-diverging nozzle of well known shape for permitting adiabatic flow of compressible fluid therein. A source 20 is connected to the inlet of converging section 14 to supply the nozzle with a compressible fluid, preferably air, at some particular entrance pressure. This fluid flows through the nozzle in the direction of arrow 22 and exits from the outlet or orifice 24 of diverging section 16. Where the tape capstan is situated in the atmosphere and the air is utilized as the working nozzle fluid, the nozzle fluid exhausts into the atmosphere at atmospheric pressure.

A hollow cylindrical capstan member 26 is rotatably attached to and about body 10 by means of bearings 28 and 30. Several rows of apertures 32 are spaced about the periphery of the capstan at a longitudinal location designed to make contact with the tape or web 38. These apertures 32 permit communication of pressure from the inner surface of the capstan to the outer surface. As best shown in FIGURE 2, a portion of the outer surface of support 10 is recessed about one-fourth of the way around its periphery to form a plenum chamber adjacent to that portion of the capstan 26 which contains apertures 32. Consequently, as capstan 26 rotates each row of apertures 32 sweeps across the stationary plenum chamber so that the pressure in the latter is communicated to the exterior surface of the capstan. Furthermore, it is desirable in most applications that at least two rows of apertures be adjacent the plenum chamber at all times in order to maintain constant clutching action as the capstan turns. Rotation of capstan 26 may be effected by a driving belt 36 which is connected to power means not shown in the drawings. Plenum chamber 34 communicates with the interior of diverging section 16 by means of a fluid passageway 40 which is connected to a port in the side wall of the nozzle.

One feature of the present invention relies upon a change in exit pressure at the nozzle output to vary the position of shock wave generation within the diverging section in order to vary the pressure differential across the tape 38. A plate 42 is parallel to orifice 24 and is approximately of the same area when viewed along the direction of fluid flow. This plate is movable in a direc-' tion along the longitudinal axis of the nozzle so as to occupy either the solid line position or the dotted line position shown in FIGURE 1. When occupying the solid line position, the fluid flow from outlet 24 is deflected so as to flow into the atmosphere (in the case of the preferred embodiment) along a path between plate 42 and body 10. If plate 42 is moved to its dotted line position, the flow emanating from the nozzle is even more restricted so that the 'backpressure increases from that present for the solid line position. Consequently, plate 42 acts as a two-position valve for varying the nozzle exit pressure.

A convenient way for moving plate 42 is the use of a permanent magnet 44 having a cantilevered pole piece 46. Plate 42 itself forms the cross member of a U or cup-shaped member having sides 48 which are slidably fitted over pole piece 46. A voice coil 50 is securely wound about sides 48 with its ends connected to a potential source selectively operated to send current of either one polarity or the other through the coil. In order to complete the magnetic circuit, a ferro-magnetic path 52 is provided for concentrating the lines of flux emanating from pole piece 46. Current of one polarity in voice coil 50 generates a magnetic field which coacts with the permanent field to attract voice coil 50 towards pole piece 46. This causes retraction of plate 42 to its solid line position, whereas current of opposite polarity in coil 50 causes its repulsion from pole piece 46 to thus position plate 42 in its dotted line position.

Before explaining the operation of the device in FIG- URES 1 and 2, a brief discussion is first given of thermodynamic principles involved in fluid flow through a converging-diverging nozzle like one shown in FIGURE 1. FIGURE 3A shows the profile of such a nozzle which is of the type permitting practically adiabatic flow of fluid therethrough. An adiabatic process is one during which no heat is transferred to or from the working fluid. In an ideal nozzle, where there is no fluid friction loss, the adiabatic process is reversible, that is, isentropic. For the isentropic process, the entropy of the fluid remains constant. An important parameter in nozzle theory is the critical pressure ratio for which maximum flow occurs. The value of the critical pressure ratio depends upon the particular working fluid and, for air, is a constant approximately equal to 0.53. There arethree locations 1, 2, and3 along the nozzle longitudinal axis at which fluid pressure values are of some importance. Location 1 is the inlet of the converging section while location 3 is the outlet of the diverging section. Location 2 is the throat of the nozzle which offers minimum cross-sectional area to fluid flow. If the exit pressure existing at location 3 is less than the critical pressure (which in turn is determined by rnultiplying the entrance pressure at location 1 by the critical pressure ratio for the particular working fluid being used), then the critical pressure itself always exists at throat location 2, and pressures lower than this critical pressure exist everywhere else in the diverging section. For such an exit pressure less than the critical pressure, the velocity of the fluid' at the throat is equal to the speed of sound in said fluid whereas the fluid velocity beyond the throat is supersonic.

To illustrate the above, refer to FIGURE 3A and as some that the entrance pressure at location 1 is a value C where the fluid utilized is air having a critical pressure ratio of 0.53. Consequently, the critical pressure for the nozzle is equal to 0.53 O=D. In FIGURE 3B it is seen that the assumed exit pressure F is lower than this critical pressure D. For this case, the pressure distribution along the longitudinal axis of the nozzle has a profile indicated by the curve C-D-F, with the throat pressure being equal to the critical pressure D. The fluid velocity at the throat is equal to the speed of sound, whereas fluid in the divergent section of the nozzle flows at supersonic speeds. In other words, for an exit pressure of value F, the fluid .adiabatically expands thus resulting in supersonic flow in the diverging section and a throat pressure equal to the fluid critical pressure D as defined above.

' If the exit pressure is greater than the fluid critical pressure, for example value E in FIGURE 3A, then the fluid is adiabatically compressed while flowing through the divergent nozzle section. For some particular value E, the pressure distribution in the nozzle assumes the path of curve C-D-E with the fluid velocity in the divergent section remaining subsonic. Now consider that the exit pressure is held at value G (FIGURE 3C) which is greater than the critical pressure D but less than pressure E previously discussed. In this case, the pres .sure distribution curve will follow the path C-DJKG.

pressure G, then the pressure distribution curve follows.

the path C-D-L-M-H.

These last two pressure distribution curves are both shown in FIGURE 30 where it is seen that the fluid flow in the diverging nozzle section has both supersonic and subsonic velocities at different locations in that section. The discontinuities J-K and LM are compression shock waves which define the boundary between supersonic and subsonic flow. In other words, for an exit pressure G, the supersonic fluid leaving the throat has a pressure distribution shown by curve D-J, whereas it suddenly changes to subsonic flow in higher pressure range as represented by curve KG. For an exit pressure H, supersonic flow abruptly changes to subsonic flow at the discontinuity L-M, with a consequent change in pressure from a relatively low value to a relatively high value. The pressure ratio existing across the shock wave may be ideally mathematically expressed as follows:

where P is the pressure immediately upstream from the shock wave front, P is the pressure immediately downstream from the shock wave front, k is the specific heat ratio of the fluid, M is the Mach number of the downstream fluid velocity, and M is the Mach number of the upstream fluid velocity. Of particular interest in FIG- URE 3C is the fact that the shock wave front can be shifted in location along the nozzle longitudinal axis according to the value of the exit pressure. As will be subsequently explained, this phenomenon is utilized in FIGURES 1 and 2 in order to selectively change the polarity of the pressure differential across the tape 38 so as to force it away from or clamp it to the capstan. However, it will be noted that the nozzle in FIGURE 1 differs slightly from the ideal profile of FIGURE 3A in that the side wall of the diverging section 16 is outwardly relieved at the two shockwave locations 41 and 43. The provision of such a relief at the origin of the shockwave (represented by the vertical wavy line) has a strengthening effect on the relative discontinuity of the pressure distribution across the front, thereby resulting in a better defined shock front. The passageway 40 can terminate in the sidewall of the downstream relief 43 since the shock front appearing at said relief will originate at its downstream edge.

The operation of the device in FIGURES 1 and 2 will now be described with particular reference to FIG- URES 30, 4A, and 4B. FIGURES 4A and 4B show the pressure distribution along the nozzle for each of two different exit pressures H and G on the order of those shown in FIGURE 30. It is assumed that source 20 provides air to the inlet of converging section 14 at .a pressure 'C which is greater than the atmospheric pressure shown by the dot-dash line. Plate 42 in its retracted solid line position is assumed to produce an exit pressure H (FIGURE 4A) which is greater than the critical pressure and of a value to result in a shock wave being generated downstream from passage 40. The pressure immediately upstream from the shock wave in FIG- URE 4A is calculated to be less than atmospheric pressure, at least in the vicinity of passage 40. This relation of the upstream pressure to the environmental pressure may be insured by a proper selection of the input pressure C and exit pressure H. Therefore, the pressure communicated to plenum chamber 34 is below atmospheric which thereupon causes tape 38 to be forced against rotating capstan 26. In being so clamped to the periphery of the capstan, tape 38 moves in the direction of its rotation.

. To stop the motion of tape 38, current of proper polarity is applied to voice coil 50 so that plate 42 is driven to its dotted line position. This position should be one to increase the exit back pressure from its initial value H to a higher value G which is calculated to cause the shock wave generation at a location upstream from passageway 40. For this condition, the pressure existing downstream from the shockwave must be above atmospheric pressure. Consequently, plate 42 in this position causes the pressure in passageway 40, and thus in plenum chamber 64, to be greater than atmospheric pressure so as to force tape 38 away from the rotating capstan.

It will be noted in FIGURE 1 that the fluid exiting from orifice 24 impinges on plate 42 in a direction parallel to the direction in which said plate has (freedom of movement. Consequently, the force exerted by this fluid jet on plate 42 tends to maintain it at, or return it to, its retracted solid line position. When plate 42 is to be moved to its dotted line position the coil 50 current must be large enough to generate a force overcoming the fluid jet force, and in all probability must be maintained for the duration of the time during which tape 38 is to be lifted away from the rotating capstan. It is desirable to have a multi-stable valve arrangement whereby the restricting plate maintains the last position to which it is moved without need for the constant presence of an energizing signal. Such an arrangement is shown in FIGURE 5, which can be used not only for controlling the exit pressure of the nozzle shown in FIGURE 1, but may also be used with other capstan nozzles operating on .a different principle from that explained above.

In FIGURE 5, the pole piece 60 of a permanent magnet 62 is placed adjacent to orifice 24 of diverging section 16. The end face or surface 166 of pole piece 60 is shaped to provide an arcuate smooth path to the exiting fluid in order to change its direction from a path which is parallel to the orifice flow axis to a path which is substantially normal to this flow axis. A hollow cylindrical sleeve member 64 is slida-bly fitted over the permanent magnet so that it is (free to move in either direction along the oriflce flow axis. A voice coil 66 is securely wound about sleeve 64 to selectively generate a magnetic field for coacting with the [field of the magnet. In order to complete the magnetic circuit of the permanent magnet, a ferromagnetic flux path 68 is provided for concentrating the flux emanating from pole piece '60. Thus, current of one polarity in voice coil 66 generates a magnetic field which coacts with the permanent magnet field in order to move sleeve 64 to the right. On the other hand, current of opposite polarity in coil 66 causes the generation of an electromagnetic field to move sleeve 64 to the position shown in FIG. 5. In order to limit the travel of sleeve 64 in either of these directions, a flange 70 may be provided about the periphery of sleeve '64. Stationary abutments 72 and 74 are provided against which flange 70 strikes when sleeve 64 moves to the left or right, respectively. A-butments 72 and 74 in turn may be attached to a viscoelastic material 76 which substantially dissipates the kinetic energy of the moving sleeve.

Another constructional feature in FIGURE 5 is the provision of a port 78 in the end surface of pole piece 60 for directing a small portion of the emerging orifice fluid into passageway 80. Radially extending from passageway 80 are two channels '81 and 82 which exit in the side surface of the permanent magnet adjacent to the inner surface of sleeve 64. Thus, an air film is created be-tween the permanent magnet and sleeve 64 over which the latter slides with but little friction.

With sleeve 64 disposed as illustrated in FIGURE 5, its end nearest orifice 24 extends past the arcuate surface 63 of the pole piece so as to reduce the effective cross-sectional area of the path into which the fluid is diverted. The fluid strikes the inner surface of sleeve 64 in a direction substantially normal thereto so that little or no force is applied to cylinder 64 in the direction in which it has freedom of motion. In other words, no horizontal force is applied by the emerging fluid which would tend to move sleeve 64 from its leftmost position to its rightmost position. This is a desirable feature since current need not be continuously applied to coil 66 after sleeve 64- has been moved to its leftmost position. If sleeve '64 is now moved to its rightmost position by a current of proper polarity, the fluid flow in its new deflected path is less restricted than before so as to decrease the exit back pressure. Again, having once moved sleeve 64 to its rightmost position, the current in coil 66 can be discontinued until it is time to once again move sleeve 64 to its leftmost position. Consequently, the absence of a horizontal load on sleeve 64 eliminates the necessity to supply a continuous signal to coil 66 in order to hold sleeve 64 in any one of its selected positions, thereby creating a multi-stable valve.

The type of nozzle operation used in moving the tape will dictate whether sleeve 64 should stop the air flow completely, or merely restrict the air flow. For example, if the nozzle in FIGURE 1 is employed, which uses the shock front to move the tape, then sleeve 64 need only restrict the air flow but not stop it completely. In this case sleeve 64 may have apertures in its periphery or may be constructed of a porous material. On the other hand, other prior art capstans may require that the nozzle exit be blocked completely in order to build up suflicient pressure to move the tape. For this case, sleeve "64 could be made of non-porous material and have a leftmost position such that it actually abuts against body 10.

The sliding sleeve arrangement shown in FIGURE 5 is especially useful for selectively permitting only one of two oppositely and constantly rotating capstans to be effective in moving magnetic tape. Such an arrange ment is illustrated in FIGURE 6 which shows a capstan 84 constantly rotating in the counterclockwise direction and a capstan 86 constantly rotating in the clockwise direction. Each capstan is mounted on a stationary body whose exterior surface contains a plenum chamber (88 for capstan 84 and 90 for capstan '86), both chambers being shown in phantom in FIGURE 6. Nozzles 92 and 94 are both stationary and are disposed about the same longitudinal axis with their orifices (facing one another. As best shown in FIGURE 7, which is a crosssectional view taken of capstan 84, the stationary support member 96 contains both bearings 98 and 100 on which the capstan rotates, as well as being the confining surface for nozzle 92 and plenum chamber 88. Communication is effected between plenum chamber 88 and the diverging section of the nozzle by means of a passageway 102 which is tapped from the nozzle side wall at a point intermediate the two shock wave locations previously discussed in connection with FIGURES 1 and 2. Apertures 104 are provided in 84, which in turn may be rotatably driven by the belt 106.

FIGURE 8 illustrates the manner of simultaneously controlling the exit pressures of nozzles 92 and 94 by a single unitary mechanism similar to that shown in FIG- URE 5. A permanent magnet is situated between the nozzle orifices along their common flow axis, with each pole piece 112 and 114 being shaped to deflect fluid emerging from the associated orifice into a path which is normal to the flow axis. A single sleeve 116- is slidably fitted about magnet 110 so that it is free to move in either direction along the orifice flow axis. A flange 118 is provided about the periphery of the sleeve for striking the abutments 120 and 122 in order to limit sleeve travel in either direction. As in FIGURE 5, abutments 120 and 122 may be attached to the viscoelastic material 124 and 126, respectively, in order to dissipate the kinetic energy of the moving sleeve. A flux path material 128 surrounds the sleeve in order to concentrate the magnetic fields which are present in the device.

A voice coil 130 is securely wound upon the outer periphery of sleeve 116 in order to selectively produce a magnetic field of one polarity or the other to thereby change the longitudinal sleeve position. In order to permit minimum current to move the sleeve, channels 132 and 134 are drilled in pole pieces 112 and 114, respectively, so that a small portion of the air emerging from the respective orifice is diverted to the space between the side surface of the pole piece and the inner surface of sleeve 116 in order to provide a film of substantially frictionless air on which the sleeve actually rides.

With sleeve 116 disposed as illustrated in FIGURE 8, that is, in its leftmost position, the air emerging from nozzle 94 is free to follow an unrestricted path to result in a back pressure value suificient to form the shock wave front downstream from the connection to plenum chamber 90. At this time, the pressure in plenum chamber 90 is below atmospheric so as to clamp tape 108 to the surface of capstan 86 and thus impart to it the left to right motion shown in FIGURE 6. At the same time, sleeve 116 projects beyond pole piece 112 in a manner to impede the progress of fluid [from nozzle 92. Consequently, the back pressure existing in nozzle 92 is sufficiently high to cause the generation of a shock wave front upstream from passageway 102, which in turn creates a pressure differential across tape 108 of a polarity to force said tape away from capstan 84. Tape 108 is therefore operatively connected to only one of the rotating capstans. Since the fluid from nozzle 92 strikes sleeve 116 at an angle substantially normal to the direction in which sleeve 116 is free to move, it is seen that no (force is applied which would tend to move sleeve 116 away from its leftmost position. There is no need to constantly maintain the energization coil 130 in order to keep sleeve 116 in its illustrated position.

When it is desired to move tape 108 in the right to left direction, coil 130 has applied to its a current of proper polarity to move sleeve 116 to its right-most position so that flange 118 abuts against material 122. For this position, sleeve 116 projects beyond pole piece 114 in order to impede the fluid from nozzle 94 and thus increase its exit pressure to a value suflicient to make the pressure in plenum chamber 90 greater than the pressure of the atmosphere. This forces tape 108 away form capstan 86 so that said capstan no longer is effective in moving the tape. At the other nozzle 92, sleeve 116 is now retracted to a position which increases the effective cross-sectional exit area through which the now diverted fluid flows. This in turn reduces the exit pressure to a value sufficient to create a vacuum in plenum chamber 88 so that tape 108 is attracted to capstan 84. The energization of voice coil 130 here need only last long enough to move sleeve 116 to its rightmost position, since the force from the fluid impinging on its inner surface from nozzle 94 acts in a direction normal to the direction in which sleeve 116 can move. Consequently, no horizontal force is applied to sleeve 116 which would tend to move it back from its rightmost position back to its leftmost position.

While preferred embodiments of the invention have been shown and described, many modifications may be made thereto by those skilled in the art without departture [from the novel principles defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as IfOllows:

1. A sheet material engaging device which comprises:

(a) a member having an outer surface adapted for contact with sheet material situated adjacent to said outer surface in an environment of some particular a pressure, said outer surface having at least one aperture therein which extends through to an inner surface of said member;

(b) a nozzle-like fluid flow conduit including a converging inputsection smoothly faired with adiverging output section;

(c) first means supplying compressible fluid at a particular entrance pressure to the inlet of said converging section, said entrance pressure being greater than the environmental pressure;

(d) second means selectively aotmable to establish either a first or a second exit pressure at the outlet of said diverging section, both of which are less than said entrance pressure but greater than the environmental pressure and the nozzle critical pressure for said fluid so that a shock wave front is generated in the fluid at either a first or a second predetermined longitudinal location, respectively, in said diverging section, with the static fluid pressure immediately upstream from said wave front being less than the environmental pressure and the static pressure immediately downstream from said wave front being greater than the environmental pressure;

(e) at least one port in the side wall of said diverging section at a longitudinal location between said first and second predetermined shock wave locations; and

( f) third means for transmitting the static fluid pressure at said port to the aperture in the inner surface of said member.

2. A device according to claim 1 wherein the side wall of said diverging section is outwardly relieved at both said first and second predetermined shock wave locations in order to produce a better defined shock front.

3. A device according to claim 2 wherein said port is located in the relieved side wall at the shock wave location which is furthest downstream.

4. A device according to claim 1 wherein the fluid from said diverging section issues into the environment via an orifice, and said second means includes guide means situated exterior to said orifice for deflecting at least a portion of the fluid issuing therefrom from a first flow path along the orifice flow axis to a second flow path substantially normal to said flow axis, with a member selectively movable in a plane substantially normal to said second flow path for obstructing the flow of fluid therein.

5. A device according to claim 4 wherein said guide means is symmetrical about said orifice flow axis such that said fluid portion is deflected to at least two opposed sides of said axis, and said obstructing member is 'a hollow sleeve entirely surrounding at least said two opposed sides of said flow axis which is movable in either direction parallel thereto.

6. A device according to claim 1 wherein said member is a movable capstan.

7. A device according to claim 1 wherein said member is a hollow cylindrical capstan mounted on said conduit for rotation about its longitudinal axis and whose outer surface having a plurality of apertures therein spaced along the direction of rotation, and said third means includes a plenum chamber located next to the inner surface of said capstan member which is of a size in the direction of rotation which is suflicient to always simultaneously register with at least two of said apertures.

8. A device according to claim 7 wherein the side wall of said diverging section is outward'ly relieved at both saidfirst and second predetermined shock wave 10- cations in order to produce a better defined shock front, and said port is located in the relieved side wall at the shock wave location which is furthest downstream.

9. A capstan device for engaging a web in order to transmit motion thereto, which comprises:

(a) a stationary nozzle-like fluid flow conduit including a converging input section smoothly faired with a diverging output section, which in turn terminates in an orifice exposed to an environment of some particular' pressure;

'(b) a hollow cylindrical capstan member mounted on said conduit for rotation about its longitudinal axis,

said capstan member having an outer surface adapted for contact with a web situated adjacent to said outer surface in said environment, said outer surface having a plurality of apertures therein spaced along the direction of rotation each of which extends through to an inner surface of said capstan member;

(c) first means supplying compressible fluid at a particular entrance pressure to the inlet of said converging section, said entrance pressure being greater than the environmental pressure;

(d) guide means situated exterior to said orifice for deflecting at least a portion of the fluid issuing therefrom from a first flow path along the orifice flow axis to a second flow path substantially normal to said flow taxis;

(e) a member selectively movable to first and second positions in a plane substantially normal to said second flow path so as to respectively establish either a first or a second exit pressure at the outlet of said diverging section, both of which are less than said entrance pressure but greater than the environmental pressure and the nozzle critical pressure for said fluid so that a shock wave front is generated in the fluid at either a first or a second predetermined longitudinal location, respectively, in said diverging section, with the static fluid pressure immediately upstream from said wave front being less than the environmental pressure and the static pressure immediately downstream from said wave front being greater than the environmental pressure;

(f) at least one port in the side wall of said diverging section at a longitudinal location between said first and second predetermined shock wave locations;

(g) a plenum chamber located next to the inner surface of said capstan member, said plenum chamber :being of a size in the direction of rotation which is sufficient to always simultaneously register with at least two of said apertures; and

(h) a passageway connecting together said port and said plenum chamber.

10. A device according to claim 1 wherein the side wall of said diverging section is outwardly relieved at at least one of said first and second predetermined shock wave locations in order to produce a better defined shock front.

11. A device according to claim 10 wherein the side wall of said diverging section is outwardly relieved at at least the shock wave location which is furthest downstream.

12. A device according to claim 1 wherein the side wall of said diverging section is outwardly relieved at at least the predetermined shock wave location which is furthest downstream in order to produce a better defined shock front and said port is located in the relieved sidewall at said last named location.

13. A device according to claim 9 wherein the side wall of said diverging section is outwardly relieved at at least one of said first and second predetermined shock wave locations in order to produce a better defined shock front.

14. A device according to claim 9 wherein the side wall of said diverging section is outwardly relieved at at least the predetermined shock wave location which is furthest downstream in order to produce a better defined shock front and said port is located in the relieved side wall at said last named location.

15. A device according to claim 14 wherein the side wall of said diverging section is further outwardly relieved at the predetermined shock wave location which is furthest upstream.

References Cited by the Examiner UNITED STATES PATENTS 2,954,911 10/ 1960 Baumeister 226 3,050,083 8/1962 Verway 137625.18 3,093,283 6/1963 Hodges 22695 3,136,336 6/1964 Priesmeyer 137-6-25.l8

M. HENSON WOOD, IR., Primary Examiner.

ROBERT B. REEVES, Examiner.

S. ALPERT, Assistant Examiner. 

1. A SHEET MATERIAL ENGAGING DEVICE WHICH COMPRISES: (A) A MEMBER HAVING AN OUTER SURFACE ADAPTED FOR CONTACT WITH SHEET MATERIAL SITUATED ADJACENT TO SAID OUTER SURFACE IN AN ENVIRONMENT OF SOME PARTICULAR PRESSURE, SAID OUTER SURFACE HAVING AT LEAST ONE APERTURE THEREIN WHICH EXTENDS THROUGH TO AN INNER SURFACE OF SAID MEMBER; (B) A NOZZLE-LIKE FLUID FLOW CONDUIT INCLUDING A CONVERGING INPUT SECTION SMOOTHLY FAIRED WITH A DIVERGING OUTPUT SECTION; (C) FIRST MEANS SUPPLYING COMPRESIBLE FLUID AT A PARTICULAR ENTRANCE PRESSURE TO THE INLET OF SAID CONVERGING SECTION, SAID ENTRANCE PRESSURE BEING GREATER THAN THE ENVIRONMENTAL PRESSURE; (D) SECOND MEANS SELECTIVELY ACTUABLE TO ESTABLISH EITHER A FIRST OR A SECOND EXIT PRESSURE AT THE OUTLET OF SAID DIVERGING SECTION, BOTH OF WHICH ARE LESS THAN SAID ENTRANCE PRESSURE BUT GREATER THAN THE ENVIRONMENTAL PRESSURE AND THE NOZZLE CRITICAL PRESSURE FOR SAID FLUID SO THAT A SHOCK WAVE FRONT IS GENERATED IN THE FLUID AT EITHER A FIRST OR A SECOND PREDETERMINED LONGITUDINAL LOCATION, RESPECTIVELY, IN SAID DIVERGING SECTION, WITH THE STATIC FLUID PRESSURE IMMEDIATELY UPSTREAM FROM SAID WAVE FRONT BEING LESS THAN THE ENVIRONMENTAL PRESSURE AND THE STATIC PRESSURE IMMEDIATELY DOWNSTREAM FROM SAID WAVE FRONT BEING GREATER THAN THE ENVIRONMENTAL PRESSURE; (E) AT LEAST ONE PORT IN THE SIDE WALL OF SAID DIVERGING SECTION AT A LONGITUDINAL LOCATION BETWEEN SAID FIRST AND SECOND PREDETERMINED SHOCK WAVE LOCATIONS; AND (F) THIRD MEANS FOR TRANSMITTING THE STATIC FLUID PRESSURE AT SAID PORT TO THE APERTURE IN THE INNER SURFACE OF SAID MEMBER. 